1. Field of the Invention
This invention relates generally to nuclear plant containment systems and, more particularly, to such a containment system that employs prefabricated component support structures.
2. Related Art
The primary components of a nuclear steam generating system are typically positioned within a containment structural system, which must be capable of resisting internal pressure and temperature increases caused by a Design Basis Accident, in which a loss of coolant is assumed, in combination with other loading requirements. The system must also be capable of providing radiation shielding during the entire life of the nuclear steam generating system, including a Design Basis Accident. In the past, these requirements have been met in several ways. One method is to employ a steel containment vessel supported on a concrete foundation mat. The steel containment forms a hermetically sealed vessel, which serves to provide leak tightness and resist the internal pressure. A concrete structure, separated from the steel vessel, usually surrounds the steel vessel in order to provide radiation shielding and protection for the steel vessel against the effects of tornadoes and other external loading. This outer concrete structure is usually supported on the same foundation mat as the steel vessel. During a Design Basis Accident, the steel vessel expands as it is subjected to internal pressure and temperature increases. Because of the space provided between the steel vessel and the outer concrete shell, the outer concrete structure is not significantly affected by a Design Basis Accident. However, both structures must be capable of withstanding seismic loads, which may be assumed to be coincident with a Design Basis Accident.
Another method employs a concrete structure, which provides the primary structural resistance to all imposed loads. The interior of the concrete structure is lined with a membrane, usually metallic, in order to provide resistance to leakage. During a Design Basis Accident, any pressure load is passed to the concrete structure, which is usually reinforced with steel bars, or pre-stressed by means of tendons, or a combination of both. A third type of composite containment is described in U.S. Pat. No. 4,175,005 and employs a combination of the two foregoing systems, i.e., a steel vessel and a lined concrete structure.
The major primary system components housed within the containment include the reactor pressure vessel, steam generators, pressurizer and main coolant pumps. These components are supported at different elevations on concrete pedestals that are poured over the liner floor above the base mat. The component supports are anchored to reinforcing bars within the concrete pedestals and extend above reinforced concrete floors to an elevation that maintains the components above the floor level. Desirably, to optimize flow, the respective components are maintained at an elevation above the core of the reactor. The extremely large amount of concrete that has to be poured, even before the components can be positioned, creates the critical path for new plant construction that can take six or more years. Reducing the construction time can considerably bring down the cost of nuclear plant construction.
Accordingly, alternate construction techniques are desired that can shorten the construction time of new plants.
These and other objects are achieved by a containment system for a nuclear reactor steam supply system with one or more primary components having a metal liner, a component support leg for supporting a primary component and an outer metal form surrounding the component support leg. The metal liner has a floor, side walls and a ceiling, which surround the nuclear steam supply system and forms a hermetically sealed compartment when an access hatch in the liner is latched in a closed position. The component support leg has one end that is directly affixed to the floor of the liner and is embedded in concrete. The component support leg extends substantially vertically to a first elevation at which the primary component is to be supported. The outer metal form contacts the concrete in which the one end of the component support leg is embedded. The outer metal form has one end affixed to the floor of the liner and extends substantially vertically to an elevation below the first elevation. Preferably, the outer metal form is capped by a reinforced concrete floor through which the component support leg extends vertically to a pre-selected component support elevation. The space between the form and the component support leg can be filled with a sand-like substance, radiation absorber material or concrete grout.
The component support leg and surrounding form can be fabricated in multiple lengths that are assembled by bolts and/or welding prior to placement in the containment system. Members perpendicular to the major axis of a support structure can be used to increase the load spreading capacity in the surrounding concrete.